lcd_st7920: Use a longer delay at the start of each command/data

It appears the st7920 requires a longer delay when switching from
command to data mode (and vice-versa).  Slower MCUs don't show a
problem because the klipper command processing time results in a
sufficient delay.  However, some of the faster MCUs can process
klipper commands fast enough that the next st7920 transfer is sent too
fast.  Add an additional delay to account for this.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

4 files changed, 33 insertions, 22 deletions

diff --git a/config/example-extras.cfg b/config/example-extras.cfg
index 1398f992..81231f75 100644
--- a/config/example-extras.cfg
+++ b/config/example-extras.cfg
@@ -539,10 +539,6 @@
 #sid_pin:
 #   The pins connected to an st7920 type lcd. These parameters must be
 #   provided when using an st7920 display.
-#chip_delay:
-#   This parameter specifies the internal command delay (in seconds)
-#   on st7920 displays. It may be necessary to increase this if the
-#   display shows garbled data. The default is 0.000020.
 
 
 # Custom thermistors (one may define any number of sections with a
diff --git a/config/generic-re-arm.cfg b/config/generic-re-arm.cfg
index 4a9c9fab..13a2c792 100644
--- a/config/generic-re-arm.cfg
+++ b/config/generic-re-arm.cfg
@@ -93,8 +93,3 @@ max_z_accel: 100
 #cs_pin: P0.16
 #sclk_pin: P0.15
 #sid_pin: P0.18
-#chip_delay needs to be set to the below for the LCD to initialise correctly.
-#chip_delay: .000040
-
-
-
diff --git a/klippy/extras/display.py b/klippy/extras/display.py
index e68c3db7..00a4777d 100644
--- a/klippy/extras/display.py
+++ b/klippy/extras/display.py
@@ -161,7 +161,9 @@ HD44780_chars = [
 # ST7920 (128x64 graphics) lcd chip
 ######################################################################
 
-ST7920_DELAY = .000020 # Spec says 72us, but faster is possible in practice
+# Spec says 72us, but faster is possible in practice
+ST7920_CMD_DELAY  = .000020
+ST7920_SYNC_DELAY = .000045
 
 class ST7920:
     char_right_arrow = '\x1a'
@@ -182,7 +184,6 @@ class ST7920:
         self.mcu = mcu
         self.oid = self.mcu.create_oid()
         self.mcu.add_config_object(self)
-        self.chip_delay = config.getfloat('chip_delay', ST7920_DELAY, minval=0.)
         self.send_data_cmd = self.send_cmds_cmd = None
         self.is_extended = False
         # framebuffers
@@ -195,9 +196,10 @@ class ST7920:
     def build_config(self):
         self.mcu.add_config_cmd(
             "config_st7920 oid=%u cs_pin=%s sclk_pin=%s sid_pin=%s"
-            " delay_ticks=%d" % (
+            " sync_delay_ticks=%d cmd_delay_ticks=%d" % (
                 self.oid, self.pins[0], self.pins[1], self.pins[2],
-                self.mcu.seconds_to_clock(self.chip_delay)))
+                self.mcu.seconds_to_clock(ST7920_SYNC_DELAY),
+                self.mcu.seconds_to_clock(ST7920_CMD_DELAY)))
         cmd_queue = self.mcu.alloc_command_queue()
         self.send_cmds_cmd = self.mcu.lookup_command(
             "st7920_send_cmds oid=%c cmds=%*s", cq=cmd_queue)
diff --git a/src/lcd_st7920.c b/src/lcd_st7920.c
index 4351d6ac..8cd76c50 100644
--- a/src/lcd_st7920.c
+++ b/src/lcd_st7920.c
@@ -12,7 +12,7 @@
 #include "sched.h" // DECL_SHUTDOWN
 
 struct st7920 {
-    uint32_t last_cmd_time, cmd_wait_ticks;
+    uint32_t last_cmd_time, sync_wait_ticks, cmd_wait_ticks;
     struct gpio_out sclk, sid;
 };
 
@@ -45,16 +45,31 @@ st7920_xmit_byte(struct st7920 *s, uint8_t data)
 static void
 st7920_xmit(struct st7920 *s, uint8_t count, uint8_t *cmds)
 {
-    uint32_t last_cmd_time=s->last_cmd_time, cmd_wait_ticks=s->cmd_wait_ticks;
-    while (count--) {
+    if (!count)
+        return;
+
+    // Send first byte (with longer delay)
+    uint32_t last_cmd_time = s->last_cmd_time, wait_ticks = s->sync_wait_ticks;
+    uint8_t cmd = *cmds++;
+    st7920_xmit_byte(s, cmd & 0xf0);
+    while (timer_read_time() - last_cmd_time < wait_ticks)
+        // Can't complete transfer until delay complete
+        irq_poll();
+    st7920_xmit_byte(s, cmd << 4);
+    last_cmd_time = timer_read_time();
+
+    // Send subsequent bytes
+    wait_ticks = s->cmd_wait_ticks;
+    while (--count) {
         uint8_t cmd = *cmds++;
         st7920_xmit_byte(s, cmd & 0xf0);
-        // Can't complete transfer until delay complete
-        while (timer_read_time() - last_cmd_time < cmd_wait_ticks)
+        while (timer_read_time() - last_cmd_time < wait_ticks)
+            // Can't complete transfer until delay complete
             irq_poll();
         st7920_xmit_byte(s, cmd << 4);
         last_cmd_time = timer_read_time();
     }
+
     s->last_cmd_time = last_cmd_time;
 }
 
@@ -80,13 +95,16 @@ command_config_st7920(uint32_t *args)
     uint32_t end = timer_read_time();
     irq_enable();
     s->last_cmd_time = end;
-    uint32_t diff = end - start, delay_ticks = args[4];
-    if (delay_ticks > diff)
-        s->cmd_wait_ticks = delay_ticks - diff;
+    uint32_t diff = end - start, sync_delay_ticks = args[4];
+    if (sync_delay_ticks > diff)
+        s->sync_wait_ticks = sync_delay_ticks - diff;
+    uint32_t cmd_delay_ticks = args[5];
+    if (cmd_delay_ticks > diff)
+        s->cmd_wait_ticks = cmd_delay_ticks - diff;
 }
 DECL_COMMAND(command_config_st7920,
              "config_st7920 oid=%c cs_pin=%u sclk_pin=%u sid_pin=%u"
-             " delay_ticks=%u");
+             " sync_delay_ticks=%u cmd_delay_ticks=%u");
 
 void
 command_st7920_send_cmds(uint32_t *args)